Static cling vinyl decorations are commonly sold as novelties that support themselves electrostatically on a window. Other polymer films may do the same on a wall. Polymeric sheets which make up such displays are readily available for use in advertising, as wall mountable easel sheets and the like. They may support themselves on a wall or window but they are incapable of supporting additional materials.
Other materials, such as certain polymeric foams and sheets are known as a way to electrostatically mount display materials. For example, U.S. Pat. No. 4,225,369 to Felchlin discloses methods of securing a poster behind a plastic sheet, the combination then being secured to a wall. Felchlin teaches that the base must be secured by wetting and then only on a smooth surface such as glass, varnished wood, and so on, but that if the base has a rough texture only temporary adhesion can occur. Also stressed is that adhesion is produced not only by static but by closely contacting of the sheet with the base. This is an adaptation of the so-called static cling method, a surface tension-atmospheric pressure method.
U.S. Pat. No. 4,741,119 describes a display board but does not indicate a method or article that will hold a poster to any kind of wall surface. The dielectric plastic sheet, if light enough, just as with a supermarket plastic bag, may be capable of supporting itself to a wall for limited periods of time but it will not adhere a poster to a wall. This patent discloses that a document clings electrostatically on the surface of a dielectric plastic backing board. The document is in turn covered by a sheet of thin plastic that "tends to cling electrostatically." When charged by manual friction, some of these films are capable of supporting themselves electrostatically to a poster and vice-versa, but none of the methods cited in this patent will hold a poster satisfactorily to a surface such as a wall.
U.S. Pat. No. 4,275,112 discloses the use of an electrostatically chargeable intermediate sheet of double charged irradiation cross-linked insulative plastic foam with a bulk-density of 2 lbs. per cubic ft. and a nominal thickness of 1/4 inch. This document teaches that the surface of the sheet should be precharged by rubbing with a wool pad, stored for several days in an envelope and recharged again before installation. We have found that the structure and method disclosed by this patent results in adhesion which lasts for a limited amount of time, and which results in adhesion for shorter and shorter periods of time each time the intermediate sheet is charged as described.
U.S. Pat. No. 4,992,121, to one of the inventors of this application, relates to the discovery that commercial electrostatic buffing materials often contain contaminants or additives that are detrimental to creating maximum polarization densities in dielectric foam materials, and that the use of such substantially oil and fat free materials greatly enhances the degree and time of adhesion for wall mounted displays.
Certain organic polymers used for polarization of electrets in research and commercial applications, in the form of films 5-50 micrometers thick, are known to hold electrostatic charges. Polarization densities may be increased even more when materials such as polyvinylidene-fluoride (PFDF) films are stretched three to five times and subjected to corona charging at room temperatures. However, such materials have not found use in commercial electrostatic mounting systems because of the practical difficulty of applying a sufficient charge, e.g. a corona charge, at the time the display is to be mounted on a wall.